While setting up your broadcast, you may find that your audio is milliseconds ahead of your video output or vice versa. Here are some steps you can take in OBS to sync your audio and video properly.
If you are noticing that your audio and video are out of sync, your first step will be to record a quick video. Within OBS, click "Start Recording" and record a video of you speaking and then clapping three times. Watch recorded video back to get a feel for how out of sync your audio is.
In the Audio Mixer section of OBS, click the gear icon to the right of your microphone input device and click "Advanced Audio Properties".
Within "Advanced Audio Properties", you will be adjusting the "Sync Offset" of your Mic/Aux. Sync Offset is used to delay audio in milliseconds. 100 to 200 ms is a great starting point for your audio offset.
Record another short video after making any adjustments and analyze the sync. Be sure to continue to adjust incrementally as needed until your audio and video are as synced up as possible.
When introducing new audio and video devices to your broadcast, it is important to retest syncing to be sure your audio and video are lining up properly.